The professional fireworks industry has employed black powder-based pyrotechnic ignition systems for many years. These systems typically use a black powder fuse—cotton string or cord impregnated with black powder—to ignite a “lift” charge, which propels the projectile high into the air. The ignition of the lift charge also ignites a second black powder fuse, which provides a time delay to allow the projectile to reach a desired height above the ground. After the time delay of the fuse, the “break” charge is ignited, causing the particular visual or auditory effect of the pyrotechnic projectile.
Although black powder-based ignition systems are relatively easy to use, the fundamental limitations of the black powder fuse prevent the industry from achieving the timing accuracy and repeatability necessary for precisely choreographed pyrotechnic displays. This is because the burn rate—and hence the delay time—for a black powder fuse can vary considerably depending on the fabrication of the fuse, the particular materials used in the construction of the fuse, and on other parameters such as the temperature of the fuse at the time of ignition. U.S. Pat. No. 5,627,338 by Poor et al. teaches that the typical accuracy of the time delay of a black powder fuse is on the order of +/−16%. Controlling the delay time for a black powder fuse to better than +/−1% is extremely difficult; and even if this accuracy could be reliably achieved, it would still contribute to a total variability of 100 milliseconds for a 5-second fuse. That is, a +/−1% variation would cause a 5-second fuse to vary by +/−0.05 seconds, or a total variability of 100 milliseconds. Tests with pyrotechnic audiences have shown that most people can detect timing differences as small as 20 milliseconds, and half the people can detect timing differences as small as 10 milliseconds. Thus, in order to achieve precisely choreographed displays for certain types of pyrotechnic shells, particularly shells with a short burst time, the variability of the fuse's time delay must be held to better than 10 milliseconds, and preferably to about 1 millisecond. A variability of 1 millisecond represents an additional factor of 100, or +/−0.01% accuracy for a 5-second fuse. Achieving such accuracy is impossible with black powder fuses.
In addition, the inherent limitations of the black powder fuse also provide a source of potential failures that present real risk to both the display operators and the proximate audience. Pyrotechnic shells can be manufactured with the lift and break charges protected relatively well from external sources of accidental ignition by the use of protective layers around the charges. However, the use of a black powder fuse for the lift charge necessitates the exposure of the black powder to the external environment of the shell. Consequently the shell becomes much more sensitive to false ignition by burning materials from nearby pyrotechnic shells, resulting in unintentional “crossfire”. If the lift charge of a shell is ignited but the time delay fuse to the break charge burns too slowly, a “hangfire” occurs, in which the shell explodes as it returns to the ground, often near the display operator or in the audience. Even more dangerous, if a hangfire explodes after the shell hits the ground, both the explosion and the falling shell itself present significant risks to the operator and audience. If a fuse fails to ignite the lift charge, but the fuse continues to burn and ignites the break charge while the shell is still on the ground, a “mortar burst” can occur, and the ignition products of the break can potentially ignite the break charges of all the adjacent shells of the display. A break charge being ignited on the ground can result in serious injury to the operating personnel as well as the destruction of the entire display.
A number of alternatives have been proposed to eliminate black powder fuses or to improve their reliability. The most notable of these involves the use of electrically operated ignition devices, commonly called “electric matches” or “e-matches”. The construction and ignition of various forms of e-matches are described in U.S. Pat. No. 5,544,585 by Duguet, U.S. Pat. No. 5,123,355 by Hans et al., U.S. Pat. No. 4,409,898 by Blix et al., U.S. Pat. No. 4,354,432 by Cannavo' et al., U.S. Pat. No. 4,335,653 by Bratt et al., U.S. Pat. No. 4,267,567 by Nygaard et al., and U.S. Pat. No. 4,144,814 by Haas et al.
The use of an e-match to replace the black powder fuse for igniting a lift charge has the advantage that the exposed electrical wires are not susceptible to false ignition by sparks or other ignition by-products. Such use of the e-match reduces the likelihood of crossfires, but does nothing to improve the timing of the break since a black powder delay fuse would still be required to ignite the break charge. On the other hand, U.S. Pat. No. 5,627,338 by Poor et al., U.S. Pat. No. 5,623,117 by Lewis, U.S. Pat. No. 5,499,579 by Lewis, U.S. Pat. No. 5,335,598 by Lewis et al., U.S. Pat. No. 4,363,272 by Simmons, U.S. Pat. No. 4,239,005 by Simmons, and U.S. Pat. No. 4,068,592 by Beuchat describe methods to delay the firing action of an e-match based on electrical or pyrotechnic delays, but none of these methods are suitable to achieving the high accuracy required for choreographed displays. A method of using an e-match is described by Poor et al. in U.S. Pat. No. 5,627,338, but even this technique is limited to about 25 milliseconds variability, which is still a factor of 25 worse than the desired 1 millisecond variability previously discussed.
A number of problems or faults can occur during the setup of a choreographed pyrotechnic display. The pyrotechnic operator cannot easily detect many of these problems. If e-matches are used to replace the black powder fuses, new problems unique to e-matches are possible. For example, if e-matches are used to ignite the black powder lift charges, the electrical connections to the e-matches may be faulty. A common practice by the industry is to connect multiple e-matches to the same ignition source to allow multiple shells to be fired at the same time. Such multiple connections are done either in parallel or in series. If multiple e-matches are wired in parallel to a single electrical ignition source, the possibility exists that some e-matches will not be connected properly. On the other hand, if multiple e-matches are wired in series, the possibility exists that the electrical ignition source will be insufficient to ignite all of the e-matches.
If e-matches are used to ignite both the lift and break charges, additional problems may develop. For example, either or both of the e-matches may have broken wires. Furthermore, since an energy source is required to fire both e-matches (and the source for the break match must travel with the projectile), the possibility exists that either energy source may be insufficient to ignite its corresponding e-match. If, for example, the lift energy source is sufficient to ignite the lift charge, but the break energy source is not sufficient to ignite the break charge, a dangerous hangfire can result, with significant risk to the pyrotechnic operator and the audience.
Accordingly, a definite need exists for a method and system for launching and detonating pyrotechnic displays, which is capable of accuracy on the order of 1 millisecond, particularly for conventional shells that use black powder for the lift charge. A need also exists for increasing the safety for both the pyrotechnic operator and the viewing audience for conventional black powder shells. A need also exists for increasing the safety for pyrotechnic shells that use e-matches to ignite the charges. The present invention satisfies these requirements and additionally provides further related advantages.